Adults often want teenagers' lives to be straightforward and protected. The trouble with life is that it's frequently neither of those. And one trouble with life for many teenagers is the prevalence of clinical depression. Indeed, levels of adolescent depression match adult levels, and any teenager in a developed country is almost certain to have a friend affected by it.

When we want to understand, nothing beats a good story, and Tabitha Suzuma's A Note of Madness joins the list of good stories about depression. It's a confident debut, with much that's original, in well-controlled and unselfconscious prose. It uses none of the shock tactics of my favourite comparable stories, Robert Cormier's I Am the Cheese, Rachel Klein's The Moth Diaries or John Marsden's So Much to Tell You. Yet its straightforwardness and stylistic restraint make it equally strong. Remarkably, it's not even particularly sad, yet it is very real.

Flynn is a star pianist at the Royal College of Music. Mental illness strikes during preparation for a special concert. His horror at watching himself lose control is palpable. Yet this is also a book about growing up. One of the most telling lines comes when Flynn thinks back a year: "Was I really there? he wondered. Could that have been the same me?" Teenagers change greatly in a year, and the speed of change is often disorienting. Regret for lost childhood can hurt. But Flynn is also very ill.

Although the story unfolds through Flynn's eyes only, the voice is third person; this provides a slight, but useful, clinical distance from his inner confusion, as we see his "madness" partly through other people's reactions. "Rami shot her a warning look with a brief, barely perceptible shake of the head" reveals his brother's thoughts, while Flynn's lack of reaction is symptomatic itself. The cleverest trick is that somehow that most unreliable of narrative voices, the mentally ill patient, becomes a supremely reliable one. Thus the reader knows much more than Flynn, even though we are seeing through Flynn's eyes.

If this book weren't so compassionate, it would be a case study, and it is indeed a clear exposition of manic depression, or bipolar illness. We even learn the specific name, bipolar two, as well as some of the drugs that treat it and the risks of taking lithium. In other hands such information could be clod-hopping, but here it feeds our fascination and feels right.

It would have been easy to provide an obvious cause from Flynn's childhood - cruel/cold parents, loss of a sibling, abandonment - but there is none. Flynn has kind though helpless parents, a compassionate and knowledgeable older brother, good friends, a stable background. The message is clear: depression can affect anyone.

Flynn's ups and downs are told in detail. When he is high, pumped full of energy, we fear for him; when he plunges into lethargy, we want to drag him from bed, feed him, care for him. When he says, "Here's to never wanting to get out of bed again", we feel hopeless. But when his brother replies, "Here's to getting reacquainted with your feelings. Here's to being able to want, without being sure you're going to get. To risk being hurt and to risk being rejected. Here's to life," suddenly we understand something important. A Note of Madness is much more than a book about depression: it's about brilliance, fear, love and living. That is its achievement, and what makes it a hearteningly good read.